tool chain allowing two-way communication between a D app and a browser - sockets

Question

I wish to have an app written in the D programming language update its display in a browser. The browser should also send input data back to the app.
I'm still quite new to programming and am confused with how sockets/websockets/servers all fit together. Can anyone suggest an approach?

Answer 1

Many thanks to gmfawcett for the link to his basic D server example which I've mated with a bare-bones websocket implementation of the version 8 spec that I found elsewhere (currently only works in Chrome 14/15, I believe). It's pretty much cut'n'paste but seems to work well enough and I expect it will be sufficient in serving my needs.
If anyone has the inclination to cast a quick eye over my code for any glaring no-nos, please feel free to do so - and thanks!
Bare-bones websocket impl: http://blog.vunie.com/implementing-websocket-draft-10
Websocket v8 spec (protocol-17): https://datatracker.ietf.org/doc/html/draft-ietf-hybi-thewebsocketprotocol-17
module wsserver;
import std.algorithm;
import std.base64;
import std.conv;
import std.stdio;
import std.socket;
import std.string;
//std.crypto: https://github.com/pszturmaj/phobos/tree/master/std/crypto
import crypto.hash.base;
import crypto.hash.sha;
struct WsServer
{
private
{
Socket s;
Socket conn;
string subProtocol;
}
this(string host, ushort port = 8080, string subProtocol = "null")
{
this.subProtocol = subProtocol;
s = new TcpSocket(AddressFamily.INET);
s.bind(new InternetAddress(host, port));
s.listen(8);
conn = s.accept();
writeln("point/refresh your browser to \"http://", host, "\" to intiate the websocket handshake");
try
{
initHandshake(conn);
}
catch (Throwable e)
{
stderr.writeln("thrown: ", e);
}
}
~this()
{
conn.shutdown(SocketShutdown.BOTH);
conn.close();
s.shutdown(SocketShutdown.BOTH);
s.close();
}
string data()
{
ubyte[8192] msgBuf;
auto msgBufLen = conn.receive(msgBuf);
auto firstByte = msgBuf[0];
auto secondByte = msgBuf[1];
// not sure these two checks are woking correctly!!!
enforce((firstByte & 0x81), "Fragments not supported"); // enforce FIN bit is present
enforce((secondByte & 0x80), "Masking bit not present"); // enforce masking bit is present
auto msgLen = secondByte & 0x7f;
ubyte[] mask, msg;
if(msgLen < 126)
{
mask = msgBuf[2..6];
msg = msgBuf[6..msgBufLen];
}
else if (msgLen == 126)
{
mask = msgBuf[4..8];
msg = msgBuf[8..msgBufLen];
}
foreach (i, ref e; msg)
e = msg[i] ^ mask[i%4];
debug writeln("Client: " ~ cast(string) msg);
return cast(string) msg;
}
void data(string msg)
{
ubyte[] newFrame;
if (msg.length > 125)
newFrame = new ubyte[4];
else
newFrame = new ubyte[2];
newFrame[0] = 0x81;
if (msg.length > 125)
{
newFrame[1] = 126;
newFrame[2] = cast(ubyte) msg.length >> 8;
newFrame[3] = msg.length & 0xFF;
}
else
newFrame[1] = cast(ubyte) msg.length;
conn.send(newFrame ~= msg);
debug writeln("Server: " ~ msg);
}
private void initHandshake(Socket conn)
{
ubyte[8192] buf; // big enough for some purposes...
size_t position, headerEnd, len, newpos;
// Receive the whole header before parsing it.
while (true)
{
len = conn.receive(buf[position..$]);
debug writeln(cast(string)buf);
if (len == 0) // empty request
return;
newpos = position + len;
headerEnd = countUntil(buf[position..newpos], "\r\n\r\n");
position = newpos;
if (headerEnd >= 0)
break;
}
// Now parse the header.
auto lines = splitter(buf[0..headerEnd], "\r\n");
string request_line = cast(string) lines.front;
lines.popFront;
// a very simple Header structure.
struct Pair
{
string key, value;
this(ubyte[] line)
{
auto tmp = countUntil(line, ": ");
key = cast(string) line[0..tmp]; // maybe down-case these?
value = cast(string) line[tmp+2..$];
}
}
Pair[] headers;
foreach(line; lines)
headers ~= Pair(line);
auto tmp = splitter(request_line, ' ');
string method = tmp.front; tmp.popFront;
string url = tmp.front; tmp.popFront;
string protocol = tmp.front; tmp.popFront;
enum GUID_v8 = "258EAFA5-E914-47DA-95CA-C5AB0DC85B11"; // version 8 spec... might change
auto sha1 = new SHA1;
sha1.put(strip(headers[5].value) ~ GUID_v8);
auto respKey = to!string(Base64.encode(sha1.finish()));
// Prepare a response, and send it
string resp = join(["HTTP/1.1 101 Switching Protocols",
"Upgrade: websocket",
"Connection: Upgrade",
"Sec-WebSocket-Accept: " ~ respKey,
"Sec-WebSocket-Protocol: " ~ subProtocol,
""],
"\r\n");
conn.send(cast(ubyte[]) (resp ~ "\r\n"));
debug writeln(resp);
}
}